Fill in the grids so that every row, every column and 3x3 box contains the digits 1 through 9. There must be a one-to-one correspondence between both twins, i. e., in all positions with a certain digit in the first grid must be in the corresponding position in the second grid also always the same digit (possibly another as in the first grid). Numbers going along grey lines must be in increasing or decreasing order from one end to the other.

Fill the grid with the digits 1 to 9. The digits represent the height of the skyscraper in each cell. Each row, column and 3x3-box has exactly one of each digit. The same digits can not touch each other diagonally. The clues along the edges tell you how many skyscrapers you can see from that vantage point.

Fill the grid with the digits 1 to 9. The digits represent the height of the skyscraper in each cell. Each row, column and 3x3-box has exactly one of each digit. The clues along the edges tell you how many skyscrapers you can see from that vantage point. The red points in the near of crosses where four cells meet each other show that the cell with the red point is greater then the three other ones.

Fill the grid with the digits 1 to 9. The digits represent the height of the Skyscraper in each cell. Each row, column and 3x3-box has exactly one of each digit. The clues along the edges tell you how many skyscrapers you can see from that vantage point. The numbers between two cells give the difference of the heights.

Fill the grid with the digits 1 to 9. The digits represent the height of the skyscraper in each cell. Each row, column and 3x3-box will have exactly one of each digit. The clues along the edges tell you how many skyscrapers you can see from that vantage point. Heights of skyscrapers must be placed according to greater (>) and less (<) signs.

Fill the grid with the digits 1 to 9. The digits represent the height of the skyscraper in each cell. Each row, column and 3x3-box has exactly one of each digit. The clues along the edges tell you how many skyscrapers you can see from that vantage point. Taking 180-degree rotational symmetry, the sum of mirrored skyscrapers must be 10.